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Structural competition between halogen bonds and lone-pair···π interactions in solution is studied using (13)C NMR combined with density functional theory calculations. Among the halogen bonds considered, only the iodine bonds and a few bromine bonds are strong enough to compete successfully with the lone-pair···π interactions., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We investigate the electron dynamics and generation of whistler‐mode waves inside a short large‐amplitude magnetic structure (SLAMS) based on Magnetospheric Multiscale Satellite observations and test particle simulations. The buildup of energetic reflected ions caused by the SLAMS's intense magnetic fields favors the resonance condition of solar wind ions of ion‐ion non‐resonant mode. This might further steepen the SLAMS, leading to the Betatron acceleration of electrons and generating the whistler‐mode waves locally ahead of the peak of the magnetic field. In regions behind the peaked magnetic field, electrons are decelerated by the convection electric field during gradient drift and the whistler‐mode waves are rapidly decayed. Our study provides new insights into electron acceleration and the generation of whistler‐mode waves near the quasi‐parallel shock. Plain Language Summary: On the quasi‐parallel side of the bow shock, ultra‐low frequency waves and nonlinear structures such as shocklet and short large‐amplitude magnetic structure (SLAMS) are commonly observed, which are powered by energetic reflected ions and form in different stages during steepening. Solar wind ions are heated significantly inside these nonlinear structures. However, what role electrons played inside these structures is full of mystery. Recent numerical simulations reveal that electron dynamics and whistler‐mode waves inside these structures are responsible for triggering bow shock reconnection on the quasi‐parallel side. In this paper, we focus on electron distributions and acceleration inside SLAMS. Electrons are accelerated/decelerated in regions prior to/after the peaked magnetic field, exciting/decaying whistler‐mode waves locally which well‐regulated the electron distribution. Our work reveals the electron dynamics inside the SLAMS and provides new insights into plasma heating and acceleration near the quasi‐parallel shock. Key Points: Whistler‐mode waves are locally generated through the first‐order resonance of the electrons inside the short large‐amplitude magnetic structure (SLAMS)SLAMS steepening primarily impacts electron acceleration and whistler‐mode wave generationElectron deceleration by the v × B electric field during gradient drift leads to whistler‐mode wave decay at the trailing edge of SLAMS [ABSTRACT FROM AUTHOR]

The C-Hal (Hal = Cl, Br, or I) bond-length change and the corresponding vibrational frequency shift of the C-Hal stretch upon the C-Hal ...Y (Y is the electron donor) halogen bond formation have been determined by using density functional theory computations. Plots of the C-Hal bond-length change versus the corresponding vibrational frequency shift of the C-Hal stretch all give straight lines. The coefficients of determination range from 0.94366 to 0.99219, showing that the correlation between the C-Hal bond-length change and the corresponding frequency shift is very good in the halogen-bonded complexes. The possible effects of vibrational coupling, computational method, and anharmonicity on the bond-length change-frequency shift correlation are discussed in detail. [ABSTRACT FROM AUTHOR]

A localized Pc4‐5 ultralow‐frequency (ULF) wave event associated with a plasmaspheric plume was observed by THEMIS‐E on the dawnside near L = 6, which was identified as a second harmonic poloidal wave. The plume was identified as a sudden density enhancement during an outbound pass. The charged particle populations in the plume have a variety of periodic modulation characteristics at different energies. First, there is an antiphase relationship between magnetic field Br and particle flux across a wide energy range both for ions and electrons (~50 keV to 1 MeV). Second, there is a 180° phase shift in the modulated ion flux within an energy range of ~2–6 keV, with negative slope dispersions of ion pitch angle distributions at ~2–6 keV and ~50–75 keV, which are characteristic of drift‐bounce resonances. Third, the lower‐energy (<32 eV) ion flux is modulated at double the wave frequency, which are the result of E × B effect. Considering the generation mechanism of this poloidal mode wave within the plume, we find that it is likely generated by drift‐bounce resonance from an unstable population of ions, due to an inward radial phase space density gradient. We suggest that the localization of waves to the plume is because the high plasma density reduces the local poloidal mode eigenfrequency, enabling a match to the drift‐bounce frequencies of these ions, and resonant energy transfer from these particles to the eigenfunction at this location. This generates the Pc4‐5 second harmonic poloidal waves at a much lower L region than would otherwise be expected. Key Points: The high‐m poloidal waves in the dawnside plume were observed by THEMIS‐EThe inward radial gradient of ~57 keV and higher plasma density enable the second harmonic poloidal wave to occur in the dawnside plumeThree types of particle flux modulations are observed simultaneously along with the wave in different energy bands [ABSTRACT FROM AUTHOR]

The separatrix region is the region between the separatrix and the reconnection jet. Due to the E×B drift and velocity filter effect in which high‐energy particles with high parallel speed can be seen prior to low‐energy particles along the field line, electrons are separated from ions. The electron dynamics in this region is of interest; however it has not been studied in detail, because of the insufficient resolution of plasma data. We present a slow separatrix crossing event observed by Magnetospheric Multiscale (MMS) satellite constellation on 1 January 2016, from the magnetosheath side with high‐resolution burst mode data. The electron edge and ion edge are clearly distinguished in the separatrix region. Two types of electron dispersion, one with a short duration (~0.3 s) and the other with a longer duration (~13 s) were detected between the electron and ion edges. The rapid dispersion (with small time scale) is mainly in the parallel direction, which might originate from a thin layer with non‐frozen‐in electrons close to the separatrix. The gradual (long time scale) dispersion is seen from parallel to perpendicular directions, which comes from the E×B drift of a curved D‐shape distribution of electrons. The width of the electron diffusion region on the magnetosheath side is estimated based on MMS observation. The observation also reveals an unexpected parallel electron beam outside of the electron edge. Wave‐particle interaction or parallel potential in the inflow region may be responsible for the generation of this electron population. Plain Language Summary: Magnetic reconnection is a process commonly occurred at the Sun, the dayside magnetopause, and in the magnetotail that changes magnetic topology, and converts electromagnetic energy into plasma kinetic and thermal energies. Due to the different parallel velocities of the particles and field line convection, electrons are separated from ions, and this creates the electron edge and ion edge in the separatrix region. These separations downstream of the X‐line widen the distance in the convection direction between the field lines involved in the reconnection. This, in turn, makes it easier for the satellite to observe the changes in the magnetic field topology and electronic dynamics during magnetic reconnection. However, high‐resolution satellite data are still required for the observation of the separatrix region in the downstream. The unprecedented high temporal and spatial resolution measurements of the Magnetospheric Multiscale (MMS) mission provide a unique opportunity to perform such studies. By analyzing the magnetic field and plasma data from MMS, this study has revealed the field line topology and electron dynamics between the electron and ion edges. Possible generation mechanisms based on the electron dynamics are also discussed in this paper. Key Points: Rapid dispersion is observed at the electron edge, indicating that electrons are decoupled from the magnetic field close to separatrixThe width of the electron diffusion region on the magnetosheath side is estimated using in situ observationsA parallel electron beam is observed outside of the separatrix in the magnetosheath for the first time [ABSTRACT FROM AUTHOR]

Abstract: Ab initio quantum mechanics methods are employed to investigate CH⋯N intermolecular interactions between NH3 as the proton acceptor and CHnX4-n (n=1,3, X=F, Cl, Br, I) as the proton donor. For the NH3⋯CH3X complexes, C–H⋯N blue-shifting H-bonds are identified and the blue shifts are about 11–26cm-1. For the NH3⋯CHX3 complexes, the stronger hydrogen bonds are found, but they are all classical H-bonds with red shifts of about 100–183cm-1. The reason of the different shift directions in different halomethanes can be successfully explained by natural bond orbital analysis. The way in which the electron density is transferred for the NH3⋯CH3X complexes differs from that for the NH3⋯CHX3 complexes, which are responsible for the blue shifts in the NH3⋯CH3X complexes but the red shifts in the NH3⋯CHX3 complexes. [Copyright &y& Elsevier]

B3LYP and MP2 methods were employed to optimize thirteen conformers of (N–Cl)-glycine using 6-311++G** basis set. Single-point MPn (n=2–4) calculations using the same basis set were carried out in order to confirm the reliabilities of B3LYP and MP2 on energies and relative stabilities for the glycine derivative. On the other hand, the effects of zero-point vibrational energy and electron correlation on the relative stabilities of different (N–Cl)-glycine conformers were discussed by comparing results from these theoretical calculations. It was found from the calculations above that B3LYP method could provide geometry structure very similar to MP2 theory for (N–Cl)-glycine. But the relative stabilities of the conformers of (N–Cl)-glycine predicted by MP2 method are in more agreement with high-level MP4(SDTQ) than B3LYP. The zero-point vibrational energy plays an important role on relative stabilities of some conformers for MP2 methods, but not for B3LYP. Significant effects of electron correlation on the relative energies of (N–Cl)-glycine conformation were observed by means of different treatments for electron correlation. Natural Bond Orbital and Atoms in Molecule analyses were performed to determine the existence of intramolecular hydrogen bond, which indicate that only three conformers have intramolecular hydrogen bonds. Furthermore, NBO is also employed to investigate quantitatively hyperconjugation in the conformers in order to account for conformational preference. Our results point out that hyperconjugations are responsible for the relative stability of most conformers. While for conformers containing hydrogen bond, the origin of relative stability comes from the balance of H-bond and hyperconjugative effect. [Copyright &y& Elsevier]